A passive optical network (PON) technology is currently a main broadband access technology. A conventional PON system is a point-to-multipoint network system based on a time division multiplexing (TDM) mechanism. Referring to FIG. 1, the PON system generally includes an optical line terminal (OLT) located on a central office side, multiple optical network units (ONU) located on a user side, and an optical distribution network (ODN) between the OLT and the ONUs. The ODN is used to distribute or multiplex data signals between the OLT and the ONUs so that the multiple ONUs can share an optical transmission path. In the PON system based on the TDM mechanism, a direction from the OLT to the ONUs is called downstream, the OLT broadcasts a downstream data stream to all the ONUs in a TDM manner, and each ONU receives only data that carries an identifier of the ONU; a direction from the ONUs to the OLT is called upstream. Because all the ONUs share the optical transmission path, in order to prevent a conflict of upstream data between the ONUs, the PON system uses a Time Division Multiple Access (TDMA) manner in the upstream direction. That is, the OLT allocates a timeslot to each ONU, and each ONU sends upstream data in strict accordance with the timeslot allocated by the OLT.
However, the PON system is affected by a time division characteristic of the TDM mechanism, and available bandwidth of a user is generally restricted. In addition, available bandwidth of a fiber itself cannot be effectively used. Therefore, emerging broadband network application service requirements cannot be satisfied. To solve such a problem and in view of compatibility with an existing PON system, a hybrid PON system that integrates a wavelength division multiplexing (WDM) technology and the TDM technology is put forward in the industry. In the hybrid PON, multiple wavelength channels are used between an OLT on a central office side and ONUs on a user side to receive and send data. That is, the hybrid PON system is a multi-wavelength PON system.
In the multi-wavelength PON system, the OLT supports data sending and receiving performed simultaneously by using multiple wavelength channels. Each ONU works on one of the wavelength channels separately. In the downstream direction, the OLT uses a downstream wavelength corresponding to each wavelength channel to broadcast downstream data to multiple ONUs that work on the wavelength channel; in the upstream direction, an ONU on each wavelength channel may send, in a timeslot allocated by the OLT, upstream data to the OLT through an upstream wavelength of the wavelength channel. In order to reduce warehousing costs, the ONU generally uses a wavelength-tunable optical transceiver component. Therefore, an operating wavelength needs to be configured for the ONU during initialization. However, if a downstream receiving wavelength or an upstream sending wavelength configured by the ONU is not supported by the OLT, the ONU cannot register successfully.